One senior White House aide told NBC News that Mattis was aware the president could choose to halt the exercises.

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"He knew that it could have been offered. The president was in the room with the leader of North Korea and made the decision,” that official said.

Trump has grown fed up with Mattis for stalling his policy choices, the report said.

While two former Trump administration officials told NBC that Trump faulted Mattis for the way in which changes to the military's policy on transgender troops unfolded, another source told the news outlet that the policy change was a lengthy push.